This invention relates to microfabrication including microfabrication of integrated circuits as well as processes involved in patterning semiconductor substrates.
In material processing methodologies (such as photolithography), creating patterned layers typically involves the application of a thin layer of radiation-sensitive material, such as photoresist, to an upper surface of a substrate. This radiation-sensitive material is transformed into a patterned mask that can be used to etch or transfer a pattern into an underlying layer on a substrate. Patterning of the radiation-sensitive material generally involves exposure by a radiation source through a reticle (and associated optics) onto the radiation-sensitive material using, for example, a photolithography system. This exposure creates a latent pattern within the radiation-sensitive material which can then be developed. Developing refers to dissolving and removing a portion of the radiation-sensitive material to yield a topographic or physical pattern. For example, developing can include removal of irradiated regions of the radiation-sensitive material (as in the case of positive photoresist), or non-irradiated regions (as in the case of negative resist) using a developing solvent. The topographic pattern can then function as a mask layer.
Preparation and development of various films used for patterning can include thermal treatment or baking. For example, a newly applied film can require a post-application bake (PAB) to evaporate solvents and/or to increase structural rigidity or etch resistance. Also, a post-exposure bake (PEB) can be executed to set a given critical dimension (CD) in a particular pattern. A PEB functions by affecting acid diffusion profiles. Post-exposure bakes can be beneficial to smooth lines and mitigate standing wave profiles. Another type of bake is a cross-linking bake which can be executed if cross-linkers (cross-linking agents) are include in a photoresist composition. Cross-linkers include agents or materials that, upon thermal activation promote cross-linking between polymers. Cross-linking a resist is one technique to protect a resist from being dissolved. Use of cross-linkers, however, can have the effect of a filler and displace other desirable resist components such as photo acid generators, photo destructive bases, and other photoactive components. Fabrication tools for coating and developing substrates typically include one or more baking modules. Some lithography processes include coating a wafer with a thin film of Bottom Anti-reflective Coating (BARC), followed by coating with a resist, and then exposing the wafer to a pattern of light as a process step for creating microchips. BARC is a thin film that is typically placed between the substrate and the resist layer to absorb remaining light rays during an exposure. This is to prevent rough edges created by reflected light rays during exposure. BARC is also used between multiple layer exposures to protect the previously created layers from being exposed again.